From the field of aerodynamics it is known that laminar flow around wings and control surfaces provides the best possible lift with at the same time the least aerodynamic resistance against, i.e. opposite to, the direction of flow. However, because of the given profile shape it is frequently not possible to ensure such a laminar flow in all the occurring flow conditions. Even in the case of constant flow conditions, the flow can separate at discontinuous locations of the profile and can become turbulent, which results in reduced lift and increased profile drag.
As is also known from aerodynamics, by continuous suction-extraction of the turbulent layer, laminarisation of the flow can be achieved to a very considerable extent. Since at cruise flight conditions any reduction in drag at the same time is also associated with considerable fuel savings, flow laminarisation can result in considerable economic advantages being achieved. Attempts have therefore already been made to achieve such flow laminarisation by providing suction-extraction apertures in the wing. In this context it is an already known measure to provide slot-shaped suction-extraction apertures or microperforations on the surface of a wing, which suction-extraction apertures or microperforations extend in spanwise direction. If such hollow components are manufactured in a production process designated superplastic deformation, in which process they are expanded with the application of interior pressure in a negative form, perforation of the surface needs to be carried out after the deformation process because otherwise it is not possible to generate, in the component, the interior pressure required for the deformation process. However, such subsequent perforations are associated with a very considerable effort in terms of work and cost.
Furthermore, known hollow profiles are associated with a further disadvantage in that holes are required in the top cover plate, which holes are designed as perforations and are used for the suction-extraction of air for the purpose of flow laminarisation. Air is suction-extracted through these perforations with a hole size of 30 to 100 m and in this manner turbulent air is steadied. However, producing the perforations is very expensive, in particular if relatively large quantities of air and/or relatively large surfaces are involved in flow laminarisation. In known methods the perforations are made in the top cover plate by means of microperforation, for example using laser technology. Depending on the technique and the required perforation quality, perforation frequencies of 100 to 300 Hz are possible in this process. If ideal flow laminarisation in a wing, a tail unit, an engine nacelle or a control flap of a commercial aircraft is assumed as a base, normally approx. 4,000,000 holes per m2 are required. At average quality this results in a production time of 4.45 hours for 4 million holes, and thus of approx. 4½ hours per square meter. Thus, producing the necessary perforations for both horizontal tail units of a commercial aircraft, with each unit measuring 7 m2, takes up a period of more than two days.
The use of known methods for producing the required perforations is associated with a further disadvantage in that, as a result of the laser technique, ridges arise at the holes, and/or surface impairments arise. With such surface impairments or ridges there is a danger of air turbulence arising and thus negatively influencing the flow. In other words, the flow becomes more turbulent again as a result of the ridges or surface impairments. The production technique would thus counteract the very objective of flow laminarisation, and would at least in part cancel it. If one is not prepared to accept this disadvantage, after completion of the perforations a further, very expensive, production step of deburring, for example by chemical etching, must follow.